1. Field of the Invention
The present invention relates to a packaging container production method, a packaging container production apparatus, and a packaging material, employed to form a packaging container for containing liquid, such as a beverage.
2. Description of the Related Art
Conventionally, when a packaging container for containing liquid, such as a beverage, is to be formed from a packaging material, which, in turn, is formed from a paper substrate, rectangular blanks are blanked from the paper substrate and are then formed into packaging containers by use of a packaging container production apparatus. Specifically, a blank is folded so as to form four panels to thereby form a tubular body of a rectangular cross section, which will become a trunk portion of a packaging container. Next, a filling machine processes one end of the tubular body so as to form the tubular body into a closed-bottomed tubular body. Subsequently, the filling machine fills the closed-bottomed tubular body with liquid and then processes the other end of the tubular body so as to close the other end, thereby yielding a container filled with liquid.
As mentioned above, a blank is folded so as to form four panels to thereby form a tubular body having a rectangular cross section. The blank has a seal allowance formed along one edge thereof. After the blank is folded to form four panels, the seal allowance and the other edge of the blank are superposed on each other, and the resultant overlap portion is sealed longitudinally to thereby form a longitudinal seal portion. Since one of the edges is located within the completed packaging container, the end face thereof is exposed to contained liquid, and thus the paper substrate comes into contact with the liquid. As a result, a certain kind of liquid may penetrate into the paper substrate through the end face, potentially causing leakage of liquid from the container.
To prevent such leakage, a folding allowance is formed along one edge of the blank, and the folding allowance is folded by 180xc2x0 so as to form a seal allowance. The seal allowance and the other edge of the blank are superposed on each other such that the folding allowance is sandwiched between the seal allowance and the other edge. The resultant overlap portion is sealed longitudinally, thereby yielding a packaging container.
FIG. 1 shows a folding step in a conventional packaging container production method.
As shown in FIG. 1, in the folding step, a folding allowance 102 is formed along one edge of a blank 101. The folding allowance 102 is folded so as to form a seal allowance.
The folding step employs a metallic die 106 having a curved groove 105 formed therein. Passing through the groove 105, the folding allowance 102 is folded by 180xc2x0 so as to form the seal allowance. Subsequently, the seal allowance and another edge 103 of the blank 101 are superposed on each other. The resultant overlap portion is sealed longitudinally so as to form a longitudinal seal portion, thereby yielding a tubular body 108 having a rectangular cross section. Thus, the end face of the other edge 103 is prevented from coming into contact with liquid, even when a packaging container is formed from the tubular body 108.
Meanwhile, when the thickness, water content, hardness, and other properties of a paper substrate vary among the blanks 101, the folded state of the folding allowance 102 varies among the blanks 101, resulting in quality deterioration of packaging containers. In order to avoid such quality deterioration, the folded state of the folding allowance 102 must be adjusted among the blanks 101. However, since the die 106 is stationary, adjusting the position thereof or modifying the shape of the groove 105 is difficult to perform.
In the folding step, the folding allowance 102 is brought into contact with the die 106 while passing through the groove 105 at a speed of 300-600 m/min. Accordingly, a large amount of paper dust is generated and contaminates the environment around the packaging container production apparatus. Also, adhering to the blank 101, paper dust may be taken into the packaging container.
Since heat is generated through contact of the die 106 with the folding allowance 102 moving at high speed, the blank 101 must be cooled. Thus, a water (or air) cooling apparatus must be employed, resulting in an increase in cost of the packaging container production apparatus.
An object of the present invention is to solve the above-mentioned problems in the conventional packaging container production apparatus and to provide a packaging container production method and apparatus which do not require a die and therefore can reduce cost and which can suppress generation of paper dust to thereby improve the quality of packaging containers. Another object of the present invention is to provide a packaging material which can be used in the packaging container production method and apparatus.
To achieve the above object, the present invention provides a packaging container production method comprising the steps of: providing a blank formed from a paper substrate and having a predetermined shape; folding a folding allowance formed along one edge of the blank to thereby form a seal allowance; and superposing the seal allowance and another edge of the blank on each other and longitudinally sealing the resultant overlap portion to thereby form a tubular body.
In the folding step, the folding allowance is pressed against a running folding belt to thereby fold the folding allowance.
Since the folding belt is used instead of a die in order to fold the folding allowance, even when the thickness, water content, hardness, and other properties of a paper substrate vary among the blanks, the folded state of the folding allowance can be stabilized through adjustment of the position of a pulley. Thus, the quality of packaging containers can be improved.
In the folding step, one side of the folding allowance is in contact with the folding belt, but friction generated therebetween is very weak because of a small difference in traveling speed between blanks and the folding belt. Further, the movement of one side of the folding allowance is restricted by the folding belt, whereas the other side of the folding allowance is not in contact with the folding belt and is thus free. Thus, the resistance of the folding belt to the travel of blanks is low, whereby the generation of paper dust is suppressed to thereby improve environmental conditions around the packaging container production apparatus. Also, entry of paper dust into a packaging container, which would otherwise result from adhesion of paper dust to a blank, can be prevented.
Since the contact between blanks and the folding belt does not involve heat generation, an apparatus for cooling the blanks is not required, thereby reducing the cost of the packaging container production apparatus.
Preferably, the seal allowance and the other edge of the blank are superposed on each other such that the folding allowance abuts the other edge.
The present invention further provides a packaging container production apparatus comprising: conveying means for conveying a blank formed from a paper substrate and having a predetermined shape while holding the blank except at one edge; folding means for folding a folding allowance formed along the one edge of the blank being conveyed to thereby form a seal allowance; and sealing means for superposing the seal allowance and another edge of the blank on each other and longitudinally sealing the resultant overlap portion.
The folding means comprises a folding belt traveling in parallel with the conveying means and disposed such that the angle of inclination thereof increases with the movement of the blank.
Preferably, the seal allowance and the other edge of the blank are superposed on each other such that the folding allowance abuts the other edge, whereby the end face of the other edge does not come into contact with liquid contained in a completed packaging container.
The present invention still further provides a packaging material comprising a paper substrate. A blank having a predetermined shape is formed from the paper substrate. A folding allowance formed along one edge of the blank is folded through pressing to thereby form a seal allowance. The seal allowance and another edge of the blank are superposed on each other, and the resultant overlap portion is sealed longitudinally to thereby form the blank into a tubular body.